Shale oil exists in organic-rich shale formations and exhibits tremendous potential for exploration and development. Shale oil exists in various occurrence states, oil phase predominantly exists in the free states within the pores of inorganic minerals and organic matter, and in the dissolved states within the condensation polymers of organic matter. Accurate delineation of the oil volume in various occurrence states is significant for the detailed reserve evaluation of shale oil reservoir. At present, the shale oil reserve is mainly evaluated on the basis of experimental tests, such as pore size analysis, vacuum-imbibition method, rock pyrolysis method or chloroform asphalt "A" method. However, due to the limitation of testing principles and conditions, these methods can not accurately characterize the volume of shale oil in different occurrence states. Based on the analysis of shale reservoir characteristics and fluid occurrence states, a theoretical model was established to calculate the volume of shale oil in various occurrence states. The model can accurately calculate the free-phase oil volumes in shale inorganic pores and organic pores, the dissolved-phase oil volume within organic matter, and total oil volume. Furthermore, it can determine the unconventional physical parameters of shale inorganic minerals and organic matter. The results show that the total organic carbon content primarily affects the volume of free-state oil in organic pores and dissolved-state oil, while the solubility of organic matter mainly impacts the volume of dissolved-state oil. The total porosity is chiefly influenced by inorganic porosity, the oil volume in inorganic pores is higher for shale rock with greater porosity, which is favorable for elastic recovery. The research results provide a theoretical basis for reservoir characterization and accurate reserve evaluation of shale oil reservoirs.